Austenitic steel alloy adapted to be welded without cracking

ABSTRACT

An austenitic steel alloy capable of being welded without cracking by the argon arc-welding process, consists of substantially 16 to 35 percent by weight chromium, 15 to 45 percent by weight nickel, 0 to 5 percent by weight molybdenum, 0 to 3 percent by weight copper, 0.1 to 1.5 percent by weight aluminum, 0.01 to 0.10 percent by weight carbon, 0.30 to 0.60 percent by weight silicon, 0 to 0.008 percent by weight calcium, 0 to 0.05 percent by weight zirconium, and manganese, titanium, sulfur and phosphorus in weight-percent concentrations within the area to the left of curve I in the graph of FIG. 2 of the drawing, the balance being iron and the usual (inevitable) impurities.

United States Patent Becker et al.

[4 1 Sept. 24, 1974 AUSTENITIC STEEL ALLOY ADAPTED TO BE WELDED WITHOUTCRACKING Inventors: Horst Becker; Gerhard Kohlert,

both of Altena, Germany Vereinigte Deutsche Metallwerke AG, Zeilweg,Germany Filed: Mar. 23, 1972 Appl. No.: 237,488

Assignee:

Foreign Application Priority Data Apr. 8, 1971 Germany 2117233 U.S. Cl.75/124, 75/128 W, 75/128 E,

75/128 Z Int. Cl. C27c 37/10 Field of Search 75/128 W, 124

3,519,419 7/1970 Gibson 75/128 W 3,563,729 4/1968 Kovach 75/128 W3,573,034 3/1971 Denhard 75/128 W 3,573,899 4/1971 Groethe 75/128 W3,594,158 7/1971 Sadowski 75/124 Primary ExaminerHyland Bizot Attorney,Agent, or Firm-l(arl F. Ross; Herbert Dubno [57] ABSTRACT An austeniticsteel alloy capable of being welded without cracking by the argonarc-welding process, consists of substantially 16 to 35 percent byweight chromium, 15 to 45 percent by weight nickel, 0 to 5 percent byweight molybdenum, 0 to 3 percent by weight copper, 0.1 to 1.5 percentby weight aluminum, 0.01 to 0.10 percent by weight carbon, 0.30 to 0.60percent by weight silicon, 0 to 0.008 percent by weight calcium, 0 to0.05 percent by weight zirconium, and manganese, titanium, sulfur andphosphorus in weightpercent concentrations within the area to the leftof curve I in the graph of FIG. 2 of the drawing, the balance being ironand the usual (inevitable) impurities.

14 Claims, 2 Drawing Figures 2.0 II Z 1 1.6 hr

7 F I 7.0 I l 1.4 l

7.0 (x) CRACK SUSCEPT/B/LITY Pmmmsvzmn 3.8 37. 846

Fig. 7

PATENIEDsemzsm s'mzuz Fig.2

. CEACK- FEE'E WELD/IB/L/TV 0.612 1 0.514 7 110 70 la 5 P=fi 12001,0.006- 0.055 abla AUSTENITIC STEEL ALLOY ADAPTED TO BE WELDED WITHOUTCRACKING FIELD OF THE INVENTION Our present invention relates toaustenitic steel alloys and, more particularly, to rust-resistant orso-called stainless steels of the nickel-chromium type which arestabilized in the sense that the crystalline configuration orinfrastructure is unaffected by welding operations, such as argon arcwelding whereby hot cracking does not occur.

BACKGROUND OF THE INVENTION Austenitic steel alloys of variouscompositions, generally containing high concentrations of nickel andchromium, have been proposed for many purposes and can be welded byargon arc-welding techniques, i.e. filler-free welding under an argonblanket or atmosphere. The compositions of such alloys are adjusted to adeltaferrite concentration of 3 to percent by weight.

The presence of delta-ferrite in an austenitic matrix is associated withdestressing of the crystal structure or infra structure in thehot-cracking range, especially when relatively small cross-sections arewelded together without fillers. It has been assumed that thedelta-ferrite acts by dissolving substance such as sulfur, phosphorus,arsenic, bismuth, selenium and tellurium which may concentrate duringthe welding process and give rise to hot cracking. The delta-ferrite,therefore, renders high concentrations of the crack-promotingconstituents less detrimental.

OBJECTS OF THE INVENTION It is the principal object of the presentinvention to provide an improved austenitic steel alloy which is high innickel concentration but free from the disadvantages of earlieraustenitic steel alloys as described above.

Another object of the invention is to provide an austenitic-alloy steelhaving low susceptibility to hot cracking upon argon arc welding withoutthe use of fillers and which is relatively inexpensive or can beproduced in an inexpensive manner.

It is also an object of the invention to provide a stabilized austeniticalloy steel which is insusceptible to weld cracking and capable ofeconomical production.

SUMMARY OF THE INVENTION These objects are attained, in accordance withour invention, with a system based upon our surprising discovery that itis possible to overcome the disadvantages of substantially irreduciblehigh concentrations of sulfur and phosphorus, by providing manganese andtitanium in a certain relationship with the phosphorus and sulfurcontent as to render an austentic steel alloy less susceptible orinsusceptible to cracking when the steel' by weight zirconium, andmanganese, titanium, sulfur and phosphorus in specific weight-percentconcentrations, the balance being iron and the usual inevitableimpurities.

DESCRIPTION OF THE DRAWING The above and other objects, features andadvantages of the present invention will become more readily apparentfrom the following description, reference being made to the accompanyingdrawing in which:

FIG. 1 is a graph of the phosphorus and sulfur concentrations plotted inpercents by weight along the ordinate, against the nickel concentrationplotted in percents by weight along the abscissa, showing the maximumpermissible values of phosphorus and sulfur in an austenitic alloy steelwhich is to be free from cracking in the manner described;

FIG. 2 is a composition diagram illustrating the principles of thepresent invention.

SPECIFIC DESCRIPTION Prior to describing the principles of the presentinvention in somewhat greater detail, a consideration of FIG. 1 is inorder. Known investigations of steels having different concentrations ofchromium, nickel sulfur and phosphore have demonstrated that anincreased nickel concentration requires a reduction in the phosphorusand sulfur concentrations if weld-cracking is to be avoided. Toillustrate this point, we have shown in FIG. 1 the maximum permissibleconcentrations of sulfur and phosphorus plotted in percent by weightalong the ordinate, in dependance upon the nickel concentration (plottedin percent by weight along the abscissa), at which weld cracking isexcluded. Phosphoric and sulfur concentrations above these levels resultin aus tenitic steel alloys susceptible to weld cracking, e.g. whensubjected to argon arc welding without filler electrodes.

Reduction of the sulfur and phosphorus concentrations, however, tolevels below those shown in FIG. 1 for most austenitic steel alloys isdifiicult, especially with bodies of increased size. For example, as themass of slab ingots increases, there is an increased risk of nonuniformdistribution of the crackinducing elements (sulfur, phosphorus, etc.) asa result of increased concentrations of these elements in certain areas.Thus, to ensure that slab ingots having a weight of more than 5 metrictons consist of material which is insusceptible to weld cracking, it isfound that the sulfur content must be adjusted to about 0.0015 percentand the phosphoric content to about 0.005 in the final produce to avoidsuch enrichment or segregation. These levels are well below thosedefined by the curves P and S of FIG. 1 and are necessary becausephosphoric and sulfur concentrations at the concentrations representedby the curves give rise to detrimental enrichment at localized areas asindicated. The reduction of the phosphoric and sulfur levels to such lowvalues is uneconomical or attainable only at considerable expense byprior-art methods.

As already noted, we are able to achieve the objects of the inventionand eliminate the disadvantages of the prior art systems as a result ofour discovery that instead of removing phosphorus and sulfur, manganeseand/or titanium are added to the alloy in certain amounts which dependupon the sulfur and phosphoric content and may be given in the graph ofFIG. 2.

Referring now to FIG. 2 of the drawing, it will be seen that we haveplotted the percent by weight of manganese and titanium (together 04)along the ordinate while the sum (6) of the sulfur and phosphorus areplotted along the bscissa. The curves 1, I1 and III define certain zoneswhich can be defined as a zone X corresponding to crack susceptibilityunderargon arc welding, a zone Y corresponding to a transition range inwhich crack susceptibility is reduced and a zone Z corresponding tocrack-free weldability, Curve 1 represents the boundary to the left ofwhich an improved austenitic steel composition is obtained to the leftof the curve, with reduced tendency toward cracking. Curve II, orcourse, represents the boundary of the zone Z, to the left of thisboundary being the region in which crack-free welding can be carried outas indicated. The curve 111 represents a linear or pseudolinearapproximation of the latter boundary curve and has been provided tofacilitate the definition of the manganese and titanium boundary. Thuswe have found that the sum of the manganese and titanium weightpercentages should be related to the sum of the phosphorus and sulfurweight percentages by the relationship (Mn% +Ti%) Z A +B P%) where (3%P%) is defined, for the present purposes, by the value [3 and (Mn% Ti%)is defined as 04. Where B ranges between 0.0065 to 0.0145 percent, A ispreferably 0.05 percent and B 100. Where B lies above 0.0145 percent, A9.48 percent and B 750.

These values have been found to be critical, as shown by the graph, fora system in which the steel contains 16 to 35 percent by weightchromium, to 45 percent by weight nickel, up to 5 percent by weightmolybdenum, up to 3 percent by weight copper, 0.1 to 1.5 weight-percentaluminum, 0.01 to 0.1 percent by weight carbon and about 0.5 percent byweight silicon, the balance being iron and, of course, the usual orunavoidable impurities.

When reference is made herein to about 0.5 percent silicon, it should benoted that the silicon concentration may range between 0.3 and 0.6percent but preferably is 0.5 percent i 0.005 percent.

Advantageously, the system contains 0.001 to 0.008 percent by weightcalcium, preferably 0.004 to 0.006 percent by weight calcium and/or 0.01to 0.05 percent by weight zirconium, perferably about 0.02 percentthereof. It has been found to be especially advantageous when themanganese concentration is approximately twice the silicon content.

SPECIFIC EXAMPLES The invention will be explained more fully by thefollowing illustrative analyses (all percentages by weight) selectedfrom a large number of investigations, in which the susceptibility toweld cracking has been tested by the so-called Focke-Wulf Test, theresults of which agreed well with practical results.

' EXAMPLE 1 A body having the following analysis:

chromium nickel aluminum manganese silicon titanium Continued 0.015carbon 0.004 sulfur 0.007 phosphorus 0.010 calcium could not be weldedwithout cracking.

EXAMPLE 2 A body having the following composition:

20.9 chromium 3 i .7 nickel 0.23 aluminum 0.80 manganese 0. 39 silicon0.44 titanium 0.01 3 carbon 0.00 sulfur 0.009 phosphorus 0.001 calcium0.01 zirconium enabled the formation of satisfactory seam welds.

EXAMPLES 3 AND 4 Bodies having the following analyses also could bewelded without difficulty.

3) chromium 21.0 4) 20.50 nickel 316 31.80 aluminum 0.14 0.32 manganese0.78 0.88 silicon 0.46 0.30 titanium 0,22 0.45 carbon 0.012 0.027 sulfur0.003 0.003 phosphorus 0.005 0.010 calcium 0.005 0.004

The charges were melted in accordance with known melting processes, forinstance, in an electric arc furnacc or induction furnace. Improvementwas obtained by a subsequent vacuum treatment but was not essen tial.The charge was preferably teemed under a protective atmosphere.

The alloys which can be welded satisfactorily thus lie in the field onthe left of the limiting curve. The curve is adjoined on the right by atransitional range, in which welding cracks may be expected. Alloys inwhich the ratio of the sulfur and phosphorus contents to the manganeseand titanium contents is on the right of this range cannot be weldedwithout cracking.

FIG. 2 indicates that the formula defines a safe limit, and the alloysmay be slightly beyond said limit without a risk of welding cracks.Specifically, no attempt has been made to find a more complicatedformula for a better approximation to the limiting curve found in thetests. The linear function which has been selected bet ter defines therelationship between the contents of sulfur and phosphorus, on the onehand, and those of manganese and titanium, on the other hand. The linearsubstitute function can be used more easily in practice. This formuladefining the limiting condition has been selected to facilitate theunderstanding, however, and is not intended to restrict the scope of theinvention.

The analysis values of the above Examples 1 to 4 are also plotted inFIG. 2.

We claim:

about 0.50 percent by weight silicon, 0.001 to 0.008-

percent by weight calcium, 0 to 0.05 percent by weight zirconium, and aneffective amount of manganese, titanium, sulfur and phosphorus limitedto the weightpercent concentrations within the area to the left of curveI in the graph of FIG. 2 of the drawing, the balance being iron and theusual inevitable impurities.

2. The alloy defined in claim 1 wherein the manganese, titanium, sulfurand phosphorus weight-percent concentrations are substantially withinthe area to the left of the curve II in the graph of FIG. 2 of thedrawing.

3. The alloy defined in claim 1 wherein the manganese, titanium, sulfurand phosphorus weight concentrations are defined by the relationship a aA (B X [3) where a is the sum of the weight percentages of manganese andtitanium, B is the sum of weight percentages of sulphur and phosphorous,A is 0.05 percent and B is 100 for ,8 0.0065 to 0.0145 percent, and A is9.48 percent and B is 750 for [3 0.0145 percent.

4. The alloy defined in claim 1 which contains at least 7. The alloydefined in claim 1 wherein the manganese content is approximately twicethe silicon content.

8. An austenitic steel alloy adapted to be welded without cracking,consisting of essentially 16 to 35 percent by weight chromium, 15 to 45percent by weight nickel, 0 to 5 percent by weight molybdenum, 0 to 3percent by weight copper, 0.1 to 1.5 percent by weight aluminum, 0.01 to0.1 percent by weight carbon, 0.30 to 0.60 percent by weight silicon,0.004 to 0.006 percent by weight calcium, 0 to 0.05 percent by weightzirconium, and an effective amount of manganese, titanium, sulfur andphosphorous limited to the weightpercentage concentrations within thearea to the left of the curve I in the graph of FIG. 2 of the drawing,the balance being iron and the usual inevitable impurities.

9. The alloy defined in claim 8 wherein the manganese, titanium, sulfurand phosphorous weightpercentage concentrations are substantially withinthe area to the left of the curve II in the graph of FIG. 2 of thedrawing.

10. The alloy defined in claim 8 wherein the silicon content is about0.50 percent by weight.

11. The alloy defined in claim 8 which contains at least 0.01 percentzirconium.

12. The alloy defined in claim 11 having a silicon content of about 0.02percent by weight.

13. The alloy defined in claim 8 wherein the manganese content isapproximately twice the silicon content.

14. An austenitic steel alloy adapted to be welded without cracking andconsisting of essentially 16 to 35 percent by weight chromium, 15 to 45percent by weight nickel, 0 to 5 percent by weight molybdenum, 0 to 3percent by weight copper, 0.1 to 1.5 percent by weight aluminum, 0.01 to0.1 percent by weight carbon, 0.3 to 0.6 percent by weight silicon,0.001 to 0.008 percent by weight calcium, 0 to 0.05 percent by weightzirconium, and an effective amount of manganese, titanium, sulfur andphosphorous limited to the weight-percentage concentrations within thearea to the left of curve I of the graph of FIG. 2 of the drawing, thebalance being iron and theusual inevitable impurities.

2. The alloy defined in claim 1 wherein the manganese, titanium, sulfurand phosphorus weight-percent concentrations are substantially withinthe area to the left of the curve II in the graph of FIG. 2 of thedrawing.
 3. The alloy defined in claim 1 wherein the manganese,titanium, sulfur and phosphorus weight concentrations are defined by therelationship Alpha > or = A + (B X Beta ) where Alpha is the sum of theweight percentages of manganese and titanium, B is the sum of weightpercentages of sulphur and phosphorous, A is -0.05 percent and B is 100for Beta 0.0065 to 0.0145 percent, and A is -9.48 percent and B is 750for Beta > 0.0145 percent.
 4. The alloy defined in claim 1 whichcontains at least 0.01 percent zirconium.
 5. The alloy defined in claim4 having a zirconium content of about 0.02 percent by weight.
 6. Thealloy defined in claim 1 having a calcium content of substantially 0.004to 0.006 percent by weight.
 7. The alloy defined in claim 1 wherein themanganese content is approximately twice the silicon content.
 8. Anaustenitic steel alloy adapted to be welded without cracking, consistingof essentially 16 to 35 percent by weight chromium, 15 to 45 percent byweight nickel, 0 to 5 percent by weight molybdenum, 0 to 3 percent byweight copper, 0.1 to 1.5 percent by weight aluminum, 0.01 to 0.1percent by weight carbon, 0.30 to 0.60 percent by weight silicon, 0.004to 0.006 percent by weight calcium, 0 to 0.05 percent by weightzirconium, and an effective amount of manganese, titanium, sulfur andphosphorous limited to the weight-percentage concentrations within thearea to the left of the curve I in the graph of FIG. 2 of the drawing,the balance being iron and the usual inevitable impurities.
 9. The alloydefined in claim 8 wherein the manganese, titanium, sulfur andphosphorous weight-percentage concentrations are substantially withinthe area to the left of the curve II in the graph of FIG. 2 of thedrawing.
 10. The alloy defined in claim 8 wherein the silicon content isabout 0.50 percent by weight.
 11. The alloy defined in claim 8 whichcontains at least 0.01 percent zirconium.
 12. The alloy defined in claim11 having a silicon content of about 0.02 percent by weight.
 13. Thealloy defined in claim 8 wherein the manganese content is approximatelytwice the silicon content.
 14. An austenitic steel alloy adapted to bewelded without cracking and consisting of essentially 16 to 35 percentby weight chromium, 15 to 45 percent by weight nickel, 0 to 5 percent byweight molybdenum, 0 to 3 percent by weight copper, 0.1 to 1.5 percentby weight aluminum, 0.01 to 0.1 percent by weight carbon, 0.3 to 0.6percent by weight silicon, 0.001 to 0.008 percent by weight calcium, 0to 0.05 percent by weight zirconium, and an effective amount ofmanganese, titanium, sulfur and phosphorous limited to theweight-percentage concentrations within the area to the left of curve Iof the graph of FIG. 2 of the drawing, the balance being iron and theusual inevitable impurities.